Conventional clips of this kind are usually produced by cutting and deep drawing a metal strip. However, the apertures between the hinge elements are inconvenient, since they reduce the mechanical strength of the clips precisely at a place where the clip is subject to severe forces. Also the hinge elements wear at this place because they rub on the pivot pin which is usually made of a very strong metal.
To obviate this disadvantage, it has already been suggested that connecting clips of this kind be prepared from a strip material having a special section, its cross-section increasing considerably at the place where the hinge elements are formed. Unfortunately, this greatly increases production costs, because a strip material having a varying thickness and a special cross-sectional shape is required.
French Patent 2 342 432 suggests that the curved part of each clip which is intended to act as a hinge element, itself be folded, the two arms of the resulting fold being placed one on another perpendicularly to the main plane of the two fixing loops. In fact, this helps to increase considerably the mechanical strength of the hinge elements, the uncoupling of each one of them on both sides, resulting in the necessary space being available for engaging the hinge elements of the clips of the other row.